Introduction, Gotchas and Guidelines while using Windows Azure AppFabric Caching service.

1. Azure App Fabric Caching
Sachin Sancheti
sachin@cumulux.com
www.cumulux.com
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2. • Introduction to Azure App Fabric Cache
• Configuration and Usage
• Session State Provider Gotchas
• Tracing
• Understanding Quota & Common Errors
• Local Cache option
• Limitations of Azure Appfabric Cache
• Guidelines
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3. • The Caching service
– is a distributed, in-memory, application cache that can be used to
accelerate the performance of Windows Azure applications
– Provided as “PaaS”
– Built on top of Windows Server
Appfabric Cache (Velocity)
• Caching Usage
– Frequently Accessed Data Caching
– ASP.Net Session State
– ASP.Net Output Caching
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4. • Configuration (.config)
– Portal Demo
• Login to Windows Azure Portal
• Create/Select the cache namespace
• Click on View Client Configuration
• This configuration provides instructions to configure Azure AppFabric
caching for data caching
– Session State Provider
– Output Caching
– .config based configuration
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5. • Configuration (Code)
– Code Block
– // Declare array for cache host. DataCacheServerEndpoint[] servers = new DataCacheServerEndpoint[1];
– servers[0] = new DataCacheServerEndpoint("demo101.cache.windows.net", 22233);
– // Setup DataCacheSecurity configuration.
– string strACSKey = "<copy and paste security key from Azure portal or from the client configuration file>";
– var secureACSKey = new System.Security.SecureString();
– foreach (char a in strACSKey)
– {
– secureACSKey.AppendChar(a);
– }
– secureACSKey.MakeReadOnly();
– DataCacheSecurity factorySecurity = new DataCacheSecurity(secureACSKey);
– // Setup the DataCacheFactory configuration.
– DataCacheFactoryConfiguration factoryConfig = new DataCacheFactoryConfiguration();
– factoryConfig.Servers = servers; factoryConfig.SecurityProperties = factorySecurity;
– // Create a configured DataCacheFactory object.
– DataCacheFactory cacheFactory = new DataCacheFactory(factoryConfig);
– // Get a cache client for the default cache.
– DataCache defaultCache = cacheFactory.GetDefaultCache();
– // Add and retrieve a test object from the default cache.
– defaultCache.Add("key", "valueobject");
– string strObject = (string)defaultCache.Get("key");
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6. • Usage Only one instance of
– Data Cache (Explicit) DataCache is created
per instance of
DataCacheFactory cacheFactory = new DataCacheFactory(); DataCacheFactory
and
dataCache = cacheFactory.GetDefaultCache(); GetDefaultCache()
returns back the
dataCache.Add(“key”,object,[Timeout]); same instance each
Object o = dataCache.Get(“key”); time
– ASP.Net Session State (Implicit)
• .config DistributedCacheSessionStateStoreProvider
– ASP.Net Output Caching (Implicit)
• .config DistributedCacheOutputCacheProvider One DataFactory
instance used per
role instance
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7. • Expiration
– By default, items in a Windows Azure AppFabric cache do not expire
– We can explicitly set a timeout while adding an item into the cache
• Eviction
– When exceeds maximum cache size, the least recently used items in the
cache are evicted
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8. • Configuration
<sessionState mode="Custom" customProvider="AppFabricCacheSessionStoreProvider">
<providers>
<add name="AppFabricCacheSessionStoreProvider"
type="Microsoft.Web.DistributedCache.DistributedCacheSessionStateStoreProvider,
Microsoft.Web.DistributedCache"
cacheName="default"
useBlobMode="true“
applicationName=“demo101”
dataCacheClientName="default" />
</providers>
</sessionState>
• Gotchas
• By default, site name is considered as applicationName
– Causes issue in Development Emulator due to different site names
for multiple instances
• Avoid temptation to change useBlobMode to “false”
– Microsoft Support declared it unsupported for Windows Azure
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9. • Client Side Tracing
– <dataCacheClient>
<tracing sinkType="DiagnosticSink" traceLevel="Verbose"/>
<!-- ... -->
</dataCacheClient>
• Request Tracking
– Used by Microsoft Support to diagnose unexpected failures
– Enabling Client Side Tracing is a must
– Each request to the Windows Azure Appfabric cache has a request identifier (GUID)
attached to it. This request identifier is available from the client-side logs
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10. • 128 MB cache for $45.00/month
• 256 MB cache for $55.00/month
• 512 MB cache for $75.00/month
• 1 GB cache for $110.00month
• 2 GB cache for $180.00/month
• 4 GB cache for $325.00/month
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11. • Memory Quota
– Cache Size selected/updated for consumption
– Surpass Situation
• After maximum size is reached the cache item eviction would
happen with LRU algorithm
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12. Bandwidth
• Network Quota Cache Size
Transactions
Per Hour
MB Per
Concurrent
Connections
• Transactions (Reset every hour) Hour
• Bandwidth (Reset every hour) 128MB 400000 1400 5
• Concurrent Connections (Static) 256MB 800000 2800 10
512MB 1600000 5600 20
1GB 3200000 11200 40
2GB 6400000 22400 80
• Surpass Situation 4GB 12800000 44800 160
– Transactions & Bandwidth
• Microsoft.ApplicationServer.Caching.DataCacheException:
ErrorCode<ERRCA0017>:SubStatus<ES0009>:There is a temporary failure. Please retry later. (The
request failed because user exceeded quota limits for this hour. If you experience this often,
upgrade your subscription to a higher one)
– Connections
• ErrorCode<ERRCA0017>:SubStatus<ES0009>:There is a temporary failure. Please retry later. (The
request failed, because you exceeded quota limits for this hour. If you experience this often, upgrade your
subscription to a higher one). Additional Information : Throttling due to resource : Connections.
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13. • Microsoft.ApplicationServer.Caching.DataCacheException:
ErrorCode<ERRCA0017>:SubStatus<ES0009>:There is a temporary failure. Please retry
later. (The request failed because user exceeded quota limits for this hour. If you
experience this often, upgrade your subscription to a higher one)
• ErrorCode<ERRCA0017>:SubStatus<ES0009>:There is a temporary failure. Please retry
later. (The request failed, because you exceeded quota limits for this hour. If you
experience this often, upgrade your subscription to a higher one). Additional Information :
Throttling due to resource : Connections.
• ErrorCode<ERRCA0017>:SubStatus<ES0006>:There is a temporary failure. Please retry
later. (One or more specified cache servers are unavailable, which could be caused
by busy network or servers. For on-premises cache clusters, also verify the following
conditions. Ensure that security permission has been granted for this client account, and
check that the AppFabric Caching Service is allowed through the firewall on all cache
hosts. Also the MaxBufferSize on the server must be greater than or equal to the
serialized object size sent from the client.)
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14. • Faster Cache
– Cache object is served from the local cache (if exists ) and saves a round
trip to AppFabric Cache Server
• Configuration
– <dataCacheClients>
<dataCacheClient name="default">
<localCache isEnabled=“true" ttlValue="300" objectCount="10000"/>
…….
</dataCacheClient>
• Supports only TimeoutBased cache invalidations. As of now doesn’t
support NotificationBased cache invalidations
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15. • The maximum size of a post-serialized object is 8 MB
• Notifications
– Notifications are not supported in Windows Azure AppFabric Caching.
This also means that you cannot use notifications to invalidate the local
cache. In Windows Azure AppFabric, local cache can use only a timeout
based invalidation policy
• Regions and Tags
– Windows Azure AppFabric Caching does not support user-created
regions or tag-based searches
• No support for Named Cache
– Supports only GetDefaultCache
• No Clear All
• No Get All
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16. • Avoid only “Cache Size Based” selection, also consider bandwidth and
connection quota too
• Implement Cache Aside Model
– Due to Eviction policy applications should be designed to anticipate that items might be
missing and require reloading at any time.
• Decorator pattern might come handy in such scenarios where one class implements the
storage with AppFabric Cache and the decorator does it for persistent storage
• Carefully Enable LocalCache
– Since it doesn’t support Notifications, application might get stale data
– Generally used for reference data e.g. Country Names, Zip Codes etc.
• DataCacheFactory
– Fewer the cache factories recreated better is the performance
– Do not let the DataCacheFactory object get disposed. The life of the DataCache object
is tied to the DataCacheFactory object
– Only one instance of DataCache is created per instance of DataCacheFactory and
GetDefaultCache() returns back the same instance each time
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17. • Plan for Quotas
– Transaction, Bandwidth Limits
• Implement Cache Aside Policy
• Be aware while load testing and plan accordingly
– Connection Limits
• Each DataCacheFactory can create a number of connections. By
default, a single DataCacheFactory will only create one connection
• maxConnectionsToServer
– Specifies the maximum number of channels to open to the cache
cluster
– <dataCacheClient name="default"
maxConnectionsToServer=“2">
• Singleton implementation would help implement one connection
per web role instance for DataCacheFactory
• Do not forget the implicit connections consumed by providers
(Session and Output Cache providers)
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18. Q&A
Thank You
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